Delay budget based forwarding in communication networks

ABSTRACT

In one embodiment, certain nodes in a computer network maintain a plurality of routing topologies, each associated with a different corresponding delay (e.g., dynamically adjusted). Upon receiving a packet with an indicated delay budget at a particular node, the node updates the delay budget based on an incurred delay up to and including the particular node since the indicated delay budget was last updated, and selects a particular routing topology on which to forward the packet based on the updated delay budget and the corresponding routing topology delays. The packet may then be forwarded with the updated delay budget on the selected routing topology, accordingly.

TECHNICAL FIELD

The present disclosure relates generally to computer networks, and, moreparticularly, to delay sensitivity for message forwarding in computernetworks.

BACKGROUND

Existing proprietary systems used in the Smart Grid space are closed andtypically only support a single application. As a result, users andoperators must deploy multiple networks to support multiple applications(e.g., one network for Automated Meter Reading (AMR), another networkfor Distribution Automation, etc.). In contrast, the Internet Protocol(IP) is an open standard that is designed to support multipleapplications simultaneously. As a result, one of the main benefits ofutilizing an IP architecture in the Smart Grid is the ability to providemulti-service networks carrying multiple simultaneously traffic flowswith different Service Level Agreements (SLAs).

Existing IP networks share a routing topology across the entire Class ofService (CoS) range. In particular, packets are marked using the IPv6Traffic Class field or Multi-Protocol Label Switching (MPLS) “EXP” fieldby the source node or the entry node (e.g., border router or gateway) inthe network using access control lists (ACLs) or deep packet inspection.The IP packet is then routed along the routing topology and the packetis queued at each hop in the corresponding queue. The link bandwidth isshared across the queues and the queues are serviced according to theparticular scheduling algorithms configured for each CoS. In addition,other congestion avoidance techniques are used to handle random packetdrops so as trigger various back-off mechanisms.

As an example, delay sensitive traffic may be assigned to a specificCoS. Packets marked with the delay-sensitive CoS are queued at each hopin a queue that is provisioned according to the targeted SLA. While theCoS mechanism is general and has been applied successfully in manyService Providers and large enterprise networks, there are somedrawbacks. The CoS mechanism requires heavy engineering techniques and adeep understanding of the network behavior in terms of applications,network topology, traffic matrix to provision the network and makeeffective use of the CoS. Furthermore, in current networks, the requireddelay is not explicitly carried in the packet itself; rather a CoS isindicated (an integer) that translates into a order of priority, whichcan hardly be mapped to the actual delay requirement for the packet.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein may be better understood by referring to thefollowing description in conjunction with the accompanying drawings inwhich like reference numerals indicate identically or functionallysimilar elements, of which:

FIG. 1 illustrates an example computer network;

FIG. 2 illustrates an example network device/node;

FIG. 3 illustrates an example packet;

FIGS. 4A-4C illustrate example delay based routing topologies in thecomputer network of FIG. 1;

FIGS. 5A-5B illustrate examples of delay budget based packet forwardingin the computer network;

FIG. 6 illustrates an example of limited delay budget application in thecomputer network;

FIG. 7 illustrates an example simplified procedure for delay budgetbased forwarding in the computer network;

FIG. 8 illustrates another example simplified procedure for delay budgetbased forwarding in the computer network, particularly regarding themanagement of network resources; and

FIG. 9 illustrates another example simplified procedure for delay budgetbased forwarding in the computer network, particularly for initiating apacket into the network with a delay sensitivity.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

According to one or more embodiments of the disclosure, certain nodes ina computer network maintain a plurality of routing topologies, eachassociated with a different corresponding delay (e.g., dynamicallyadjusted). Upon receiving a packet with an indicated delay budget at aparticular node, the node updates the delay budget based on an incurreddelay up to and including the particular node since the indicated delaybudget was last updated, and selects a particular routing topology onwhich to forward the packet based on the updated delay budget and thecorresponding routing topology delays. The packet may then be forwardedwith the updated delay budget on the selected routing topology,accordingly.

Description

A computer network is a geographically distributed collection of nodesinterconnected by communication links and segments for transporting databetween end nodes, such as personal computers and workstations, or otherdevices, such as sensors, etc. Many types of networks are available,ranging from local area networks (LANs) to wide area networks (WANs).LANs typically connect the nodes over dedicated private communicationslinks located in the same general physical location, such as a buildingor campus. WANs, on the other hand, typically connect geographicallydispersed nodes over long-distance communications links, such as commoncarrier telephone lines, optical lightpaths, synchronous opticalnetworks (SONET), synchronous digital hierarchy (SDH) links, orPowerline Communications (PLC) such as IEEE 61334, IEEE P1901.2, andothers. In addition, a Mobile Ad-Hoc Network (MANET) is a kind ofwireless ad-hoc network, which is generally considered aself-configuring network of mobile routes (and associated hosts)connected by wireless links, the union of which forms an arbitrarytopology.

Smart object networks, such as sensor networks, in particular, are aspecific type of network having spatially distributed autonomous devicessuch as sensors, actuators, etc., that cooperatively monitor physical orenvironmental conditions at different locations, such as, e.g.,energy/power consumption, resource consumption (e.g., water/gas/etc. foradvanced metering infrastructure or “AMI” applications) temperature,pressure, vibration, sound, radiation, motion, pollutants, etc. Othertypes of smart objects include actuators, e.g., responsible for turningon/off an engine or perform any other actions. Sensor networks, a typeof smart object network, are typically shared-media networks, such aswireless or PLC networks. That is, in addition to one or more sensors,each sensor device (node) in a sensor network may generally be equippedwith a radio transceiver or other communication port such as PLC, amicrocontroller, and an energy source, such as a battery. Often, smartobject networks are considered field area networks (FANs), neighborhoodarea networks (NANs), etc. Generally, size and cost constraints on smartobject nodes (e.g., sensors) result in corresponding constraints onresources such as energy, memory, computational speed and bandwidth.Correspondingly, a reactive routing protocol may, though need not, beused in place of a proactive routing protocol for smart object networks.

FIG. 1 is a schematic block diagram of an example computer network 100illustratively comprising nodes/devices 200 (e.g., labeled as shown,“root,” “11,” “12,” . . . “35,” and described in FIG. 2 below)interconnected by various methods of communication. For instance, thelinks 105 may be wired links, or else a type of shared media (e.g.,wireless links, PLC links, etc.), where certain nodes 200, such as,e.g., routers, sensors, computers, etc., may be in communication withother nodes 200, e.g., based on distance, signal strength, currentoperational status, location, etc. Those skilled in the art willunderstand that any number of nodes, devices, links, etc. may be used inthe computer network, and that the view shown herein is for simplicity.

Data packets 140 (e.g., traffic and/or messages sent between thedevices/nodes) may be exchanged among the nodes/devices of the computernetwork 100 using predefined network communication protocols such ascertain known wired protocols, wireless protocols (e.g., IEEE Std.802.15.4, WiFi, Bluetooth®, etc.), PLC protocols, or other shared-mediaprotocols where appropriate. In this context, a protocol consists of aset of rules defining how the nodes interact with each other.

FIG. 2 is a schematic block diagram of an example node/device 200 thatmay be used with one or more embodiments described herein, e.g., as anyof the nodes shown in FIG. 1 above. The device may comprise one or morenetwork interfaces 210 (e.g., wired, wireless, PLC, etc.), at least oneprocessor 220, and a memory 240 interconnected by a system bus 250, aswell as a power supply 260 (e.g., battery, plug-in, etc.).

The network interface(s) 210 contain the mechanical, electrical, andsignaling circuitry for communicating data over links 105 coupled to thenetwork 100. The network interfaces may be configured to transmit and/orreceive data using a variety of different communication protocols. Inaddition, the interfaces 210 may comprise a media access control (MAC)layer module, as well as other layers, such as the physical or “PHY”layer, as will be understood by those skilled in the art. Generally, forpurposes of illustration herein, a simplified “delay process” 212 hasbeen shown Note, further, that the nodes may have two different types ofnetwork connections 210, e.g., wireless and wired/physical connections,and that the view herein is merely for illustration. Also, is while thenetwork interface 210 is shown separately from power supply 260, for PLCthe network interface 210 may communicate through the power supply 260,or may be an integral component of the power supply. In some specificconfigurations the PLC signal may be coupled to the power line feedinginto the power supply.

The memory 240 comprises a plurality of storage locations that areaddressable by the processor 220 and the network interfaces 210 forstoring software programs and data structures associated with theembodiments described herein. Note that certain devices may have limitedmemory or no memory (e.g., no memory for storage other than forprograms/processes operating on the device and associated caches). Theprocessor 220 may comprise necessary elements or logic adapted toexecute the software programs and manipulate the data structures 245. Anoperating system 242, portions of which are typically resident in memory240 and executed by the processor, functionally organizes the device by,inter alia, invoking operations in support of software processes and/orservices executing on the device. These software processes and/orservices may comprise routing process/services 244, other variousprotocol specific processes, and one or more illustrative applications248 that may generate delay sensitive packets, as described herein.

It will be apparent to those skilled in the art that other processor andmemory types, including various computer-readable media, may be used tostore and execute program instructions pertaining to the techniquesdescribed herein. Also, while the description illustrates variousprocesses, it is expressly contemplated that various processes may beembodied as modules configured to operate in accordance with thetechniques herein (e.g., according to the functionality of a similarprocess). Further, while the processes have been shown separately, thoseskilled in the art will appreciate that processes may be routines ormodules within other processes.

Routing process (services) 244 contains computer executable instructionsexecuted by the processor 220 to perform functions provided by one ormore routing protocols, such as proactive or reactive routing protocolsas will be understood by those skilled in the art. These functions may,on capable devices, be configured to manage a routing/forwarding table(a data structure 245) containing, e.g., data used to makerouting/forwarding decisions. In particular, in proactive routing,connectivity is discovered and known prior to computing routes to anydestination in the network, e.g., link state routing such as OpenShortest Path First (OSPF), orIntermediate-System-to-Intermediate-System (ISIS), or Optimized LinkState Routing (OLSR). Reactive routing, on the other hand, discoversneighbors (i.e., does not have an a priori knowledge of networktopology), and in response to a needed route to a destination, sends aroute request into the network to determine which neighboring node maybe used to reach the desired destination. Example reactive routingprotocols may comprise Ad-hoc On-demand Distance Vector (AODV), DynamicSource Routing (DSR), DYnamic MANET On-demand Routing (DYMO), etc.Notably, on devices not capable or configured to store routing entries,routing process 244 may consist solely of providing mechanisms necessaryfor source routing techniques. That is, for source routing, otherdevices in the network can tell the less capable devices exactly whereto send the packets, and the less capable devices simply forward thepackets as directed.

Notably, mesh networks have become increasingly popular and practical inrecent years. In particular, shared-media mesh networks, such aswireless or PLC networks, etc., are often on what is referred to asLow-Power and Lossy Networks (LLNs), which are a class of network inwhich both the routers and their interconnect are constrained: LLNrouters typically operate with constraints, e.g., processing power,memory, and/or energy (battery), and their interconnects arecharacterized by, illustratively, high loss rates, low data rates,and/or instability. LLNs are comprised of anything from a few dozen andup to thousands or even millions of LLN routers, and supportpoint-to-point traffic (between devices inside the LLN),point-to-multipoint traffic (from a central control point such at theroot node to a subset of devices inside the LLN) and multipoint-to-point traffic (from devices inside the LLN towards a central controlpoint).

An example protocol specified in an Internet Engineering Task Force(IETF) Internet Draft, entitled “RPL: IPv6 Routing Protocol for LowPower and Lossy Networks” <draft-ietf-roll-rpl-19> by Winter, at al.(Mar. 13, 2011 version), provides a mechanism that supportsmultipoint-to-point (MP2P) traffic from devices inside the LLN towards acentral control point (e.g., LLN Border Routers (LBRs) or “rootnodes/devices” generally), as well as point-to-multipoint (P2MP) trafficfrom the central control point to the devices inside the LLN (and alsopoint-to-point, or “P2P” traffic). RPL (pronounced “ripple”) maygenerally be described as a distance vector routing protocol that buildsa Directed Acyclic Graph (DAG) for use in routing traffic/packets 140,in addition to defining a set of features to bound the control traffic,support repair, etc. Notably, as may be appreciated by those skilled inthe art, RPL also supports the concept of Multi-Topology-Routing (MTR),whereby multiple DAGs can be built to carry traffic according toindividual requirements.

Also, a DAG is a directed graph having the property that all edges(and/or vertices) are oriented in such a way that no cycles (loops) aresupposed to exist. All edges are contained in paths oriented toward andterminating at one or more root nodes (e.g., “clusterheads or “sinks”),often to interconnect the devices of the DAG with a largerinfrastructure, such as the Internet, a wide area network, or otherdomain. In addition, a Destination Oriented DAG (DODAG) is a DAG rootedat a single destination, i.e., at a single DAG root with no outgoingedges. A “parent” of a particular node within a DAG is an immediatesuccessor of the particular node on a path towards the DAG root, suchthat the parent has a lower “rank” than the particular node itself,where the rank of a node identifies the node's position with respect toa DAG root (e.g., the farther away a node is from a root, the higher isthe rank of that node). Note also that a tree is a kind of DAG, whereeach device/node in the DAG generally has one parent or one preferredparent. DAGs may generally be built (e.g., by a DAG process and/orrouting process 244) based on an Objective Function (OF). The role ofthe Objective Function is generally to specify rules on how to build theDAG (e.g. number of parents, backup parents, etc.).

As noted above, existing proprietary systems used in the Smart Gridspace are closed and typically only support a single application. As aresult, users and operators must deploy multiple networks to supportmultiple applications (e.g., one network for Automated Meter Reading(AMR), another network for Distribution Automation, etc.). In contrast,the Internet Protocol (IP) is an open standard that is designed tosupport multiple applications simultaneously. As a result, one of themain benefits of utilizing an IP architecture in the Smart Grid is theability to provide multi-service networks carrying multiplesimultaneously traffic flows with different Service Level Agreements(SLAs).

Existing IP networks share a routing topology across the entire Class ofService (CoS) range. In particular, packets are marked using the IPv6Traffic Class field or Multi-Protocol Label Switching (MPLS) “EXP” fieldby the source node or the entry node (e.g., border router or gateway) inthe network using access control lists (ACLs) or deep packet inspection.The IP packet is then routed along the routing topology and the packetis queued at each hop in the corresponding queue. The link bandwidth isshared across the queues and the queues are serviced according to theparticular scheduling algorithms configured for each CoS. In addition,other congestion avoidance techniques are used to handle random packetdrops so as trigger various back-off mechanisms.

As an example, delay sensitive traffic may be assigned to a specificCoS. Packets marked with the delay-sensitive CoS are queued at each hopin a queue that is provisioned according to the targeted SLA. While theCoS mechanism is general and has been applied successfully in manyService Providers and large enterprise networks, there are somedrawbacks. The CoS mechanism requires heavy engineering techniques and adeep understanding of the network behavior in terms of applications,network topology, traffic matrix to provision the network and makeeffective use of the CoS.

Note that the bandwidth allocation to each queue is often allocated in astatic fashion (except for one/two optional preemptive queue), andtraffic classification is performed according to network administratorrules. Furthermore, the CoS serves as an intermediate mapping betweenthe application and the choice of forwarding/routing behavior in thenetwork. As a result, not only must the network be configured tounderstand the CoS mechanisms, but also the application wherebyCoS-to-application mapping involves complex tasks at the edge of thenetwork. In particular, the CoS does not itself state what kind ofservice the application is requesting. Instead, the CoS is simply amarking that has mutual agreement between the application and network onits semantics.

Delay Budget Forwarding

The techniques herein propose a different approach for specifyingservice levels for delay-sensitive traffic. In particular, rather thanutilizing a CoS marking, the techniques herein involve marking eachpacket with a delay budget that forwarders process hop-by-hop. Byincluding a delay budget, an application 248 can explicitly indicate therequired service level for a particular packet without relying on theCoS level of indirection. Furthermore, as described in the details thatfollow, this mechanism allows the network to dynamically adapt totime-varying application requirements and network characteristics.

In particular, according to one or more embodiments herein, forwardingpackets based on a delay budget may be achieved by including aper-packet delay budget directly in the packet itself, subtracting thecommunication delay incurred at each hop, computing multiple routingtopologies with different path delays, choosing an appropriate routingtopology when forwarding a packet based on the delay budget within thepacket, and, optionally, dynamically allocating and releasing resourcesat the PHY/MAC layer to adjust the path delays for different routingtopologies based on observed state when forwarding packets with delaybudgets.

Said differently, according to one or more specific embodiments of thedisclosure as described in detail below, certain nodes in a computernetwork maintain a plurality of routing topologies, each associated witha different corresponding delay. Upon receiving a packet with anindicated delay budget at a particular node, the node updates the delaybudget based on an incurred delay up to and including the particularnode since the indicated delay budget was last updated, and selects aparticular routing topology on which to forward the packet based on theupdated delay budget and the corresponding routing topology delays. Thepacket may then be forwarded with the updated delay budget on theselected routing topology, accordingly.

Illustratively, the techniques described herein may be performed byhardware, software, and/or firmware, such as in accordance with thedelay process 212, which may contain computer executable instructionsexecuted by a processor (e.g., specific to the network interface 210 orelse a centralized processor 220) to perform functions relating to thenovel techniques described herein, e.g., in conjunction with one or moreapplications 248. For example, the techniques herein may be treated asextensions to conventional protocols, such as the various PHY and/or MACcommunication protocols (or other network-layer protocols), and as such,may be processed by similar components understood in the art thatexecute those protocols, accordingly.

Operationally, a first component of the techniques herein consists ofmarking each packet with a delay budget. FIG. 3 illustrates a simplifiedview of a packet as may be appreciated by those skilled in the art, andextended according to the techniques herein. In particular, a packet maygenerally comprise one or more headers 310 and a payload 320 containingthe data / information to be transmitted. Within the header 310 is theinformation used to forward the packet, such as a source address 312, adestination address 314, and/or various encapsulation fields, errorcorrection fields, checksums, etc. Additionally, for use as describedherein, a “delay” field 316 may also be located within the one or moreheaders 310.

According to the techniques herein, when generating a packet, anapplication 248 may insert an acceptable communication delay (i.e., the“delay budget”) for delivering the packet 300 to its destination. In atraditional network stack, the application layer may provide the delaybudget when submitting a packet to the transport layer, e.g., based ondetermining the associated delay budget from the application 248initiating the packet. Note that in one embodiment, this delay budget316 field may be included using a new IPv6 Hop-by-Hop Option, orpotentially within an existing packet field.

As described herein, when forwarding a packet 300, the forwardersubtracts the amount of delay incurred by the current hop. For example,to account for queuing delay (that is, associated with the forwarderbetween receiving the packet and forwarding the packet), the forwardermay timestamp the packet upon receiving it, take another timestampbefore sending it, and subtracts the difference from the delay budgetincluded in the packet. To account for transmission delay to reach theforwarder (in addition or alternatively), a previous hop (previousforwarder) may timestamp the packet before transmission, and thereceiving node (forwarder) may record the timestamp after receiving thepacket, and then subtracts the difference from the delay budget includedin the packet. In this manner, the receiving node may determine the timeto reach the node itself since the indicated delay budget was lastupdated (e.g., particularly in the event the previous hop was not a nodethat included a timestamp, as detailed below). Note that this embodimentgenerally requires neighboring devices to be time synchronized, thoughit should also be noted that this is common for devices in manynetworks, such as in channel-hopping (frequency-hopping) packetnetworks. Other methods (e.g., Network Time Protocol, “NTP”) may also beused to achieve time synchronization.

In effect, the delay budget is updated at each (so configured) hop toindicate the remaining amount of delay the packet can incur in order tosatisfy the application's request. In other words, upon receiving apacket with an indicated delay budget 316 at a particular node, thedelay budget is updated based on an incurred delay up to and includingthe particular node since the indicated delay budget 316 was lastupdated. As described below, this delay budget is used to driveforwarding decisions at each hop, that is, to select a particularrouting topology (of a plurality of routing topologies) on which toforward the packet based on the updated delay budget and correspondingrouting topology delays.

It is worth noting that the techniques herein are not proposingmodification to the routing decision algorithms according to a delayrouting metric. Instead, the techniques herein select pre-computedrouting topologies based on the delays to reach destinations using aparticular topology (e.g., specifically known delays, or elsehierarchical levels of general delay sensitivity). Note also that thisdelay budget approach dramatically differs from existing techniques thatuse CoS markings to classify packets, since for CoS markings to beeffective, the network must be manually provisioned to meet particularSLAs for each CoS.

According to one or more embodiments herein, a second component involvesmaintaining a plurality of routing topologies within a computer network,each of the routing topologies associated with a different correspondingdelay. Specifically, the network nodes (e.g., routing process 244) maythus be configured to compute different routing topologies (RTs) toachieve different path delays, e.g., a plurality of routing topologieswith different delays based on corresponding characteristic trade-offs.For example, a first routing topology with lower path delay maysacrifice other metrics (e.g., energy) to achieve a lower path delay.However, a routing topology with a higher path delay may incur higherpath delays to avoid resource-constrained devices (e.g., battery-powered, memory-constrained, etc.).

Note that in one embodiment, each routing topology may associated with aparticular delay sensitivity, e.g., a fast, medium, and slow (or anyother variously defined delay sensitivities, such as very sensitive,moderately sensitive, or indifferent, etc.), while in anotherembodiment, the corresponding delay associated with the routingtopologies are particular to one or more specific destinations withinthe computer network. For example, each node may need to only compute adelay to one or more root nodes, or one or more other nodes of interest(e.g., aggregators, collectors, etc.). For instance, many Smart Grid orsensor network topologies are multi-point-to-point (MP2P) topologies,and as such, each node need only compute the delay for each topology tothe single point.

As shown in FIGS. 4A-4C, the network computes a path delay along a setof N routing topologies 410, “RT(1),” “RT(2),” “RT(3),” etc. (shown inFIG. 4A, 4B, and 4C, respectively). Note that each of the differenttopologies as shown need not be link diverse (and are generally not nodediverse, as the intention is not diversity, and each node should haveconnectivity). In particular, the links may be shared with the sameassociated delay (e.g., shared queues), and the delay may be based onusing different links to different nodes, or else the same links (ordifferent links) may be associated with different delays based onvarious internal resources dedicated to the packet flows, such asforwarding queues, processing pipelines, etc.

For example, a protocol such as RPL has the ability to compute multipleDAGs (“instances” in RPL terminology) where each DAG is optimizedaccording to one or metrics and constraints. In the context of theembodiments herein, each DAG may be optimized for the path delay metric,but may utilize different constraints (e.g., little or no constraintsfor the RT that provides minimal path delay and one or more constraintsfor the RT that provides some additional delay). Alternatively, thetechniques herein may use other known techniques to provide differentrouting topologies, such as MTR approaches in OSPF or ISIS, etc.

In one embodiment, the network may perform dynamic resource allocationto achieve a lower or higher path delay for a routing topology. Inparticular, devices may locally monitor the traffic flowing through anddetermine whether or not the requested delay budgets are being met. Ifthe delay budgets are not being met for a proportion of traffic (saiddifferently, detecting that a proportion of delay budgets not satisfiedis above a threshold), the device may request additional resources toachieve a lower delay bound (reduce the corresponding delays). Forexample, the device may allocate (or request allocation of) additionalcommunication slots in a time-synchronized network (e.g.,frequency-hopping timeslots), a number of queuing buffers, etc. In onespecific embodiment, the device may also request change (e.g.,relaxation) of a routing topology determination constraint, such aswhether energy constrained devices may be used, etc. Note also thatconversely, if the delay budgets are being met with sufficient margin(e.g., a proportion satisfied above a threshold), the device may release(or request release of) resources to reduce resource consumption, and tothus relax the corresponding associated delays for the routingtopologies as they are not needed at the time. In still anotherembodiment, a central device (e.g., a root node, a Network ManagementSystem or “NMS,” a head-end application, etc.) may collect informationfrom routers such as the proportion of packets with unsatisfied delayrequirements and may allocate (or release) io resources as needed toachieve the appropriate path delay for each routing topology.

According to the embodiments herein, when forwarding a packet, theforwarder subtracts the communication delay incurred by the current hopfrom the delay budget 316, and by inspecting the remaining delay budget,the forwarder will determine what routing topology to use in order tomeet the remaining delay budget for the packet 300.

FIGS. 5A and 5B illustrate examples of packet processing in accordancewith one or more embodiments herein. For instance, as shown in FIG. 5A,assume that node 31 (e.g., an application 248 on node 31) generates apacket 300 with a given delay budget that node 31 assumes can be met byforwarding it on the routing topology RT(3) to the root node.Accordingly, node 32 receives the packet, updates the delay budget(based on the transmission to node 32, and the processing by node 32),and determines still that RT(3) is suitable. Once at node 22, however,perhaps an exceptional delay has occurred in the network, and node 22'sassessment of the updated delay budget 316 in the packet is that RT(3)is no longer suitable. As such, node 22 may switch the packet to RT(2).Note that routing topology changes need not be incremental, and nodesmay immediately select an appropriate topology. Once at node 12 onRT(2), node 12 may further assess the delay budget 316 as not suitablefor RT(2), and may forward the node directly to the root device onRT(1).

Note further that while in many configurations, there is little need fora node in communication with the root to have different topologies tothe root node, such as shared-media networks operating on the samechannel, various other techniques may actually allow and benefit fromhaving multiple topologies, such as wired networks, independentpair-wise frequency-hopping sequence networks, etc., and as such, itcannot be assumed that any transmission from nodes 11, 12, or 13 will beheard by the root device, and as such, nodes 11, 12, and 13 may havedifferent resources (e.g., queues) allocated to reaching the root node,accordingly.

If the forwarder does not have a routing topology that can satisfy thedelay budget, thus determining a condition that there is no routingtopology to satisfy the updated delay budget, the forwarder may recordthe condition and forward the packet along the best routing topologyavailable (i.e., one with a shortest delay). Also, if the forwardernotices that the condition occurs too frequently, it may trigger theallocation of additional resources (e.g., additional communicationslots, additional queuing buffers, etc.) to achieve lower path delays,as noted above. Further, where the associated delays are specific to aparticular destination, and are not simply a hierarchical level of delaysensitivity, if it is determined that there is no known delay for aparticular destination 314 of the packet 300, e.g., if the only knowndestination is the root node, and the packet is destined to node 34,then the packet may be forwarded on a default routing topology (such as,depending upon network configuration, the slowest, the fastest, or anyparticular routing topology in between).

Also, FIG. 5B illustrates another example of packet processing, forexample, where there is excess delay budget in the packet for aparticular routing topology. For instance, assume that node 35 initiatesa packet 300 with an associated delay budget 316. If node 35 determinesthat routing topology RT(1) is needed to reach the root in time, thenthe packet may be forwarded on RT(1) directly to node 24. Once at node24, however, perhaps due to over-estimation of the actual delay or dueto a change (reduction) in the delay to reach node 24 (or for node 24 toprocess the packet), then node 24 may redirect the packet onto alonger-delayed routing topology, RT(2), and forwards the packet to node23. However, once at node 23, an additional delay may be encounteredthan what was expected by node 24, and node 23 may decide to place thepacket back on the faster topology RT(1), and the packet is sentdirectly to the root node, hopefully before expiration of the associateddelay budget 316.

Notably, in an illustrative embodiment, each node in the network 100 isconfigured to forward the packets 300 based on a delay budget. However,in an alternative embodiment, only a subset of all nodes in the computernetwork 100 are configured to update the delay budget and select routingtopologies on which to forward the packet. In this instance, as notedabove, the delay budget 316 is updated based on the incurred delay sincethe indicated delay budget was last updated by another node of thislimited subset.

FIG. 6 illustrates an example of this alternative embodiment, where onlynodes 31 and 23 of a particular packet's path are configured to performdelay budget based routing. For instance, node 31 may select aparticular topology (e.g., RT(3) based on a long delay budget),forwarding the packet 300 to node 32. From node 32, following RT(3)results in the packet being forwarded to node 22, and then 23, eachmerely forwarding the packet in a conventional manner, without anyregard to the delay (i.e., on the same topology on which the packet wasreceived). Once at node 23, however, the delay budget 316 may beupdated, and it may be determined that node 31's assessment of the delayalong RT(3) had under-estimated delay (e.g., due to variance incongestion, queue lengths, etc.). If node 23 determines that RT(3) is nolonger suitable for the associated delay budget 316 of the packet, node23 may then select an appropriate routing topology, e.g., RT(1), andthus attempts to forward the packet toward the destination within theindicated delay budget, accordingly.

FIG. 7 illustrates an example simplified procedure for delay budgetbased forwarding in a computer network in accordance with one or moreembodiments described herein. The procedure 700 starts at step 705, andcontinues to step 710, where, as described in greater detail above, anode in a network 100 computes or maintains a plurality of routingtopologies 410, each of the routing topologies associated with adifferent corresponding delay. Upon receiving a packet 300 in step 715,that is, one with an indicated delay budget 316, the particular nodeupdates the delay budget in step 720 based on an incurred delay up toand including the particular node since the indicated delay budget waslast updated, as detailed above.

Based on the updated delay budget and the corresponding routing topologydelays, in step 725 the receiving node selects a specific on which toforward the packet. Note that as described above, in the event there isno known destination delay in step 730, then in step 735 a defaulttopology is selected. Also, if in step 740 there is no satisfactorytopology, then in step 745 a best topology may be selected, e.g., andthe occurrence may be recorded in order to maintain network resourcesaccordingly. In step 750, the packet 300 is forwarded with the updateddelay budget 316 on the selected routing topology, and the procedure 700ends in step 755, notably with the opportunity to revise routingtopologies or receive further packets with/without revising routingtopologies, accordingly.

In addition, FIG. 8 illustrates another example simplified procedure fordelay budget based forwarding in a computer network in accordance withone or more embodiments described herein, particularly regarding themanagement of network resources. That is, the procedure 800 dynamicallyadjusts resource allocation for one or more of the routing topologiesbased on at least of either a proportion of satisfied delay budgets anda proportion of unsatisfied delay budgets. Specifically, procedure 800starts at step 805, and continues to step 810, where, as described ingreater detail above, the proportion of delay budgets satisfied versusunsatisfied is monitored. If the proportion (or number) of unsatisfiedbudgets crosses a configured threshold in step 815, then in step 820additional resources may be allocated (e.g., requested) for one or moreof the routing topologies 410 to reduce the corresponding associateddelays, as previously described in detail. Conversely, if in step 825the proportion of satisfied delay budgets is greater than some specifiedthreshold, then in step 830 one or more resources may be released fromone or more of the routing topologies to relax the correspondingassociated delays. The procedure 800 illustratively ends in step 835,though may continue to monitor for satisfied and unsatisfied delaybudgets during the processing of delay budget based forwarding in thecomputer network.

Moreover, FIG. 9 illustrates another example simplified procedure fordelay budget based forwarding in a computer network in accordance withone or more embodiments described herein, particularly for initiating apacket into the network with a delay sensitivity. The procedure 900starts at step 905, and continues to step 910, where, as described ingreater detail above, a delay sensitive packet 300 may be generated,e.g., in response to a request from an application 248. An associateddelay budget 316 may be then be inserted into the packet in step 915,and in step 920 the generating node selects a routing topology 410 onwhich to forward the packet based on the delay budget and correspondingrouting topology delays. Accordingly, as described above, the nodeforwards the packet with the delay budget in step 925 on the selectedrouting topology. The procedure 900 ends in step 930, and may restart inresponse to a newly generated packet.

It should be noted that while certain steps within procedures 700-900may be optional as described above, the steps shown in FIGS. 7-9 aremerely examples for illustration, and certain other steps may beincluded or excluded as desired. Further, while a particular order ofthe steps is shown, this ordering is merely illustrative, and anysuitable arrangement of the steps may be utilized without departing fromthe scope of the embodiments herein. Moreover, while procedures 700-900are described separately, certain steps from each procedure may beincorporated into each other procedure, and the procedures are not meantto be mutually exclusive.

The novel techniques described herein, therefore, provide for delaybudget based forwarding in a computer network. In particular, byforwarding packets based on a delay budget as described above, thetechniques herein allow for efficient network performance management,and allow dynamic resource allocation based on observed network stateand the observed traffic characteristics, thus reducing the amount ofmanual configuration required. In addition, the techniques hereinclassify packets using a simple delay budget indication, rather thanClass of Service (CoS) marking, thus dramatically simplifying theconfiguration and provisioning of the network. Note also that while MTRin classic IP networks is optimized against a specific routing metric(e.g., delay, bandwidth, etc.), the packets in classic IP MTR are notswitched between delay-based topologies according to a required delaybudget, as described herein.

While there have been shown and described illustrative embodiments thatprovide for delay budget based forwarding in a computer network, it isto be understood that various other adaptations and modifications may bemade within the spirit and scope of the embodiments herein. For example,the embodiments have been shown and described herein with relation toLLNs. However, the embodiments in their broader sense are not aslimited, and may, in fact, be used with other types of constrainednetworks and/or associated protocols. In addition, the techniques aboveare not limited to wireless or other shared-media communication (e.g.,PLC), and may be applied to wired networks as well.

The foregoing description has been directed to specific embodiments. Itwill be apparent, however, that other variations and modifications maybe made to the described embodiments, with the attainment of some or allof their advantages. For instance, it is expressly contemplated that thecomponents and/or elements described herein can be implemented assoftware being stored on a tangible (non-transitory) computer-readablemedium (e.g., disks/CDs/etc.) having program instructions executing on acomputer, hardware, firmware, or a combination thereof. Accordingly thisdescription is to be taken only by way of example and not to otherwiselimit the scope of the embodiments herein. Therefore, it is the objectof the appended claims to cover all such variations and modifications ascome within the true spirit and scope of the embodiments herein.

1. A method, comprising: maintaining a plurality of routing topologieswithin a computer network, each of the routing topologies associatedwith a different corresponding delay; receiving a packet with anindicated delay budget at a particular node; updating the delay budgetbased on an incurred delay up to and including the particular node sincethe indicated delay budget was last updated; selecting a particularrouting topology of the plurality of routing topologies on which toforward the packet based on the updated delay budget and thecorresponding routing topology delays; and forwarding the packet withthe updated delay budget on the particular routing topology.
 2. Themethod as in claim 1, wherein the corresponding delay associated withthe routing topologies are particular to one or more specificdestinations within the computer network, and wherein selecting theparticular routing topology comprises: determining that there is noknown delay for a particular destination of the packet; and in response,forwarding the packet on a default routing topology.
 3. The method as inclaim 1, further comprising, in response to determining a condition thatthere is no routing topology to satisfy the updated delay budget:selecting a particular routing topology of the plurality of routingtopologies with a shortest delay; and recording the condition.
 4. Themethod as in claim 1, further comprising: dynamically adjusting resourceallocation for one or more of the routing topologies based on at leastof either a proportion of satisfied delay budgets and a proportion ofunsatisfied delay budgets.
 5. The method as in claim 4, wherein resourceallocation is selected from a group consisting of: a number ofcommunication slots in a frequency hopping sequence; a number of queuingbuffers, and one or more routing topology determination constraints. 6.The method as in claim 1, further comprising: detecting that aproportion of delay budgets not satisfied is above a threshold; and inresponse, allocating additional resources for one or more of the routingtopologies to reduce the corresponding associated delays.
 7. The methodas in claim 1, further comprising: detecting that a proportion of delaybudgets satisfied is above a threshold; and in response, releasingresources from one or more of the routing topologies to relax thecorresponding associated delays.
 8. The method as in claim 1, whereinupdating the delay budget comprises subtracting at least one of either atransmission delay to reach the particular node since the indicateddelay budget was last updated and a queuing delay associated with theparticular node between receiving the packet and forwarding the packet.9. The method as in claim 1, further comprising: computing the pluralityof routing topologies with different delays based on correspondingcharacteristic trade-offs.
 10. The method as in claim 1, wherein therouting topologies are selected from a group consisting of: directedacyclic graph (DAG) instances; and multi-topology routing (MTR)instances.
 11. The method as in claim 1, further comprising: generatinga second packet by the particular device; inserting an associated delaybudget into the second packet; and forwarding the second packet.
 12. Themethod as in claim 11, further comprising: determining the associateddelay budget from an application initiating the packet at the particularnode.
 13. The method as in claim 1, wherein the particular node is afirst node of a subset of all nodes in a computer network that areconfigured to update the delay budget and select routing topologies onwhich to forward the packet, and wherein the delay budget is updatedbased on the incurred delay since the indicated delay budget was lastupdated by a second node of the subset.
 14. An apparatus, comprising:one or more network interfaces to communicate in a computer network; aprocessor coupled to the network interfaces and adapted to execute oneor more processes; and a memory configured to store a process executableby the processor, the process when executed operable to: maintain aplurality of routing topologies within the computer network, each of therouting topologies associated with a different corresponding delay;receive a packet with an indicated delay budget; update the delay budgetbased on an incurred delay up to and including the apparatus since theindicated delay budget was last updated; select a particular routingtopology of the plurality of routing topologies on which to forward thepacket based on the updated delay budget and the corresponding routingtopology delays; and forward the packet with the updated delay budget onthe particular routing topology.
 15. The apparatus as in claim 14,wherein the corresponding delay associated with the routing topologiesare particular to one or more specific destinations within the computernetwork, and wherein the process when executed to select the particularrouting topology is further operable to: determine that there is noknown delay for a particular destination of the packet; and in response,forward the packet on a default routing topology.
 16. The apparatus asin claim 14, wherein the process when executed is further operable to:determine a condition that there is no routing topology to satisfy theupdated delay budget; and in response, select a particular routingtopology of the plurality of routing topologies with a shortest delayand record the condition.
 17. The apparatus as in claim 14, wherein theprocess when executed is further operable to: dynamically adjustresource allocation for one or more of the routing topologies based onat least of either a proportion of satisfied delay budgets and aproportion of unsatisfied delay budgets.
 18. The apparatus as in claim14, wherein the process when executed to update the delay budget isfurther operable to: subtract at least one of either a transmissiondelay to reach the apparatus since the indicated delay budget was lastupdated and a queuing delay associated with the apparatus betweenreceiving the packet and forwarding the packet.
 19. The apparatus as inclaim 14, wherein the process when executed is further operable to:generating a second packet by the particular device; inserting anassociated delay budget into the second packet; and s forwarding thesecond packet.
 20. A tangible, non-transitory, computer-readable mediahaving software encoded thereon, the software when executed by aprocessor on a particular node operable to: maintain a plurality ofrouting topologies within the computer network, each of the routingtopologies associated with a different corresponding delay; receive apacket with an indicated delay budget; update the delay budget based onan incurred delay up to and including the particular node since theindicated delay budget was last updated; select a particular routingtopology of the plurality of routing topologies on which to forward thepacket based on the updated delay budget and the corresponding routingtopology delays; and forward the packet with the updated delay budget onthe particular routing topology.